Downstream processing is a major challenge in bioprocess industry due to the high complexity of bio-suspensions itself, the low concentration of the product and the stress sensitivity of the valuable target molecules. A multitude of unit operations have to be joined together to achieve an acceptable purity and concentration of the product. Since each of the unit operations leads to a certain product loss, one important aim in downstream-research is the combination of different separation principles into one unit operation. In the current work a dead-end membrane process is combined with an electrophoresis operation. In the past this concept has proven successfully for the concentration of biopolymers. The present work shows that using different ultrafiltration membranes in a two-sided electro-filter apparatus with flushed electrodes brought significant enhancement of the protein fractionation process. Due to electrophoretic effects, the filtration velocity could be kept on a very high level for a long time, furthermore, the selectivity of a binary separation process carried out exemplarily for bovine serum albumin (BSA) and lysozyme (LZ) could be greatly increased; in the current case up to a value of more than 800.Thus the new two-sided electro-ultrafiltration technique achieves both high product purity and short separation times.